Geonav 11C, GPS mushroom antenna failed, is there a battery in there?

[vas]

evening all,

my mate with a Geonav11C came back, last time was a broken NMEA+ in pin on the plotter socket, now he says cannot get a fix.
Tried it here with the other NMEA0183 antenna I had spare, takes an awful lot of time to get a fix, hope it's going to work, so I bet it's the mushroom.
Is it safe to assume there's a CR2032 disk battery in there (as in other gps mushrooms)?
if so, anyone remember how it opens, not in an extremely convenient spot, so rather I have an idea before getting up there in the radar arch!

and no, don't know what mushroom is up there, have seen it, don't remember seeing any model/numbers on it and don't have a pic either.
Boat is 15nm away (or one hour by car) and I'm not going there soon.

cheers

V.

 

[vas]

as expected other gps mushroom worked, albeit took half the night to get a fix!
now comes up with this:

date is 15th Jan 2004, shouldn't that be picked up by the sat system and update internal time of the plotter?
As I said, mushroom I'm testing now had a new battery fitted a couple of years ago, just to be safe, opened it up last night and was measuring 3.05V so should be good enough.

cheers

V.

 

[ProDave]

I don't think the GPS system transmits actual date, just a code, and the date / time rolls over every couple of decades or something. My Chartplotter lets you set the year to correct for that, not sure if it then updates the GPS aerial or not?

I have always found a GPS system not used for a long time takes a long time to get it's first fix. I wonder if that is why the spare aerial took a long time because it has not been used for a while? Power it down and try again and see if it gets it's fix quicker. It was explained rather poorly in one user manual as it does not know where to look for the satellites if it has not been used for a while.

 

[vas]

thanks Dave,

yes, I've read all that about cold boot, warm and hot boot. Indeed this morning I could turn it off and then 1h later on again and would get an immediate fix.
Thinking of taking the lot to my boat (400metres away...) and see if the same lot will get an immediate fix, hope so.
still leaves me clueless on why the other antenna onboard my mates P45 is not working/giving a fix.
oh well!

V.

 

[andsarkit]

The GPS signal has a partial date with the weeks counted up to 1024 = 2^10. This comes to 19.6 years when the count will repeat. Better GPS receiver software will overcome this but many older systems will give an error on the date and because of this the almanac information will be wrong and it will take a long time to get a fix.
You need to check that there is not a slight position error associated with the date error.

 

[vas]

thanks @andsarkit

brings back memories of older threads in here and elsewhere.
Surely enough, turned off power at 9AM, fired it up now (9PM) and took around 4mins to get a fix, although the screen was showing enough sats (albeit different # to the ones it had in the morning) and their strength in black and not red:


OK, so I cannot set time on the plotter (guess no backup battery there) and interesting that such old mushrooms are practically redundant and although they work, have to be replaced (or the whole system replaced!) as getting a new fix in 2h is not really acceptable (imho)

Next step trying to figure out if this mushroom can be opened without breaking it to check and replace it's battery!
any ideas?


and


I'd have thought a bayonet type of mount between top and bottom part?
searching the web without even knowing what the model of this thing is is not v.helpful!

cheers
V.

 

[vas]

belated update on this...

opened the mushroom up (OK, technically butchered it!) water ingress, not looking v.good, scrapped it.
Mate installed Raywhatever 125 (iirc) mushroom in place of the old one, routed a new cable (didn't have to but likes to make his life difficult...) wired it up, worked.
All that in late Oct.
Went to pick the boat and bringing it back to Volos port two weeks later, nada, no fix, no way no matter how long we waited. No big deal doing 12nm coastal in flat seas at 7kn, but would be nice to fix it!

Wondering if the rollover 1024 weeks thing has caught up for good the system and the plotter is scrap. Will spend Sat morning in the marina between mine and his boat doing various little jobs, so will get it running first and see if it will get a fix in 5-6h.
I see that Navman have a patch, quick google didn't come up with anything re Geonav, so wonder if anyone else has such an old plotter and if it works fine.
We are in the med so tides not issue, mag variation probably has, wonder how much though...

cheers

V.

 

[andsarkit]

It seems a shame to scrap it if the plotter just requires a good GPS input.
The date/time comes from the NMEA 0183 sentence from the 'antenna' so a new antenna should fix that problem. Some older plotters just have an RF receiving antenna and the decoding is done in the plotter. In that case the plotter would be scrap but yours should be OK.
I have just got one of these and it seems to work fine picking up a position quite quickly.

Note the 4800 baud RS232 version and it needs a 5v supply.
They do a mushroom 12v version as well which might be more suitable.
GPS receiver
Are you sure you have the correct connections? It looks like you need pins 3 & 4 of the 9pin connector. You can power the 'antenna' from pins 7 & 8.

 

[vas]

thanks,

as I said I'm going to have another go tomorrow, at worse rip it off and bring both antenna and gps at home and try them again.
It was working last time I had it again here at home and worked once when my mate wired it all up.
Good (and cheap!) find this mushroom, will probably order one just in case.
Worse case I'll wire the ray 125 first to my computer and see what it reports time/date wise (if it reports!) and go from there.

cheers

V.

 

[PaulRainbow]

thanks,

as I said I'm going to have another go tomorrow, at worse rip it off and bring both antenna and gps at home and try them again.
It was working last time I had it again here at home and worked once when my mate wired it all up.
Good (and cheap!) find this mushroom, will probably order one just in case.
Worse case I'll wire the ray 125 first to my computer and see what it reports time/date wise (if it reports!) and go from there.

cheers

V.

If that's the Raystar 125, they suffer from the rollover problem too and according to Raymarine there is no fix.

 

[vas]

just back from the boat, slightly confused!

turned on both Geonav plotters:
one on lower helm, one on f/b with separate gps mushrooms each. The lower helm 7in one still has the original mushroom on the arch, the 11in has the "new" Ray125 next to it.
( @PaulRainbow boat is same as yours P45 first gen)
Within a minute both had a fix, go figure!
Both think that today 16.03.2024 is the 31.07.2004 which from my rough calcs is consistent with the 1024 weeks (or 19.69years)
For the record back in Sept 23 same plotter (with fix) was showing Jan2004, so dates change albeit with a slight delay
Both have decent 3D fix:
7in indoors:


11in f/b:


worked at home (500metres from the position the boat is now) in Aug.
gave it to my mate to fit it onboard 15nm away. Fitted it, tested it worked in Sept.
in early Nov went with Dimitris to bring the boat back, never got a fix. Unplugged replugged multiple times, left it on for ever, then drove at 7kn all the way, nothing, never got it.

Wont do anything, just ignore it for now

cheers

V.

 

[PaulRainbow]

just back from the boat, slightly confused!

turned on both Geonav plotters:
one on lower helm, one on f/b with separate gps mushrooms each. The lower helm 7in one still has the original mushroom on the arch, the 11in has the "new" Ray125 next to it.
( @PaulRainbow boat is same as yours P45 first gen)
Within a minute both had a fix, go figure!

Obviously a man with good taste

Wont do anything, just ignore it for now

cheers

V.

Good thinking